Recently, interest in measures against global warming, energy saving, environmental pollution and the like has been increasing. Further, interest is shifting from conventional automobiles, which burn fossil fuels and discharge carbon dioxide, to hybrid automobiles that combine a gasoline engine and an electric motor and electric automobiles that run on only an electric motor. Thus, to make hybrid automobiles and electric automobiles run efficiently, there is a need for development of a high-voltage, high energy-capacity, and high-energy density battery.
The nickel-hydrogen secondary batteries, lithium-ion batteries and the like that are used in such electric automobiles need to have a high energy density, and have a mounting space that is as small as possible. Consequently, for a high-voltage high-capacity battery, a plurality of cells is connected in series or in parallel and a battery pack device is used that connects several to several dozen or several hundred cells together.
A battery cell configuring such a battery pack can generate heat from internal reactions. Since the performance and life of a battery pack greatly depend on the temperature environment, and deterioration can be pronounced at high temperatures, cooling methods have been proposed (cf., Patent Documents 1 to 3).
Concerning the methods described in Patent Documents 1 to 3, problems such as cooling efficiency and increased size of the apparatus have been pointed out. As a method to replace these methods, a battery pack device in which thermally conductive members formed in a sheet shape (plate shape) from a soft material that has thermal conduction properties and electrical insulation properties are arranged between battery cells has been disclosed (Patent Document 4).